171 research outputs found
Marcatili's Lossless Tapers and Bends: an Apparent Paradox and its Solution
Numerical results based on an extended BPM algorithm indicate that, in
Marcatili's lossless tapers and bends, through-flowing waves are drastically
different from standing waves. The source of this surprising behavior is
inherent in Maxwell's equations. Indeed, if the magnetic field is correctly
derived from the electric one, and the Poynting vector is calculated, then the
analytical results are reconciled with the numerical ones. Similar
considerations are shown to apply to Gaussian beams in free space.Comment: 4 pages, figures include
AFLOW for alloys
Many different types of phases can form within alloys, from highly-ordered
intermetallic compounds, to structurally-ordered but chemically-disordered
solid solutions, and structurally-disordered (i.e. amorphous) metallic glasses.
The different types of phases display very different properties, so predicting
phase formation is important for understanding how materials will behave. Here,
we review how first-principles data from the AFLOW repository and the aflow++
software can be used to predict phase formation in alloys, and describe some
general trends that can be deduced from the data, particularly with respect to
the importance of disorder and entropy in multicomponent systems.Comment: Small AFLOW review submitted to special issue. 6 pages, 4 picture
AFLOW-CCE for the thermodynamics of ionic materials
Accurate thermodynamic stability predictions enable data-driven computational
materials design. Standard density functional theory (DFT) approximations have
limited accuracy with average errors of a few hundred meV/atom for ionic
materials such as oxides and nitrides. Thus, insightful correction schemes as
given by the coordination corrected enthalpies (CCE) method, based on an
intuitive parameterization of DFT errors with respect to coordination numbers
and cation oxidation states present a simple, yet accurate solution to enable
materials stability assessments. Here, we illustrate the computational
capabilities of our AFLOW-CCE software by utilizing our previous results for
oxides and introducing new results for nitrides. The implementation reduces the
deviations between theory and experiment to the order of the room temperature
thermal energy scale, i.e. ~25 meV/atom. The automated corrections for both
materials classes are freely available within the AFLOW ecosystem via the
AFLOW-CCE module, requiring only structural inputs.Comment: Small review of AFLOW-CCE for a special issue on computational
modules. 10 pages, 6 figures, 6 table
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